The present invention relates to a thermoelectric generator, and more particularly, to a thermoelectric generator for converting thermal energy of exhaust from an internal combustion engine to electric energy.
The generation of electric power using a thermoelectric generation element, which converts thermal energy to electric energy, is known in the prior art. The thermoelectric generation element takes use of the Seeback effect in which the temperature difference between two ends (high temperature portion and low temperature portion) of a metal or semiconductor piece generates a potential difference between the high temperature and low temperature portions of the metal or semiconductor piece. A larger temperature difference increases the electric power generated by the thermoelectric generation element.
FIG. 1 shows an example of the structure of a thermoelectric generation element. As shown in FIG. 1, the thermoelectric generation element includes n-type and p-type semiconductors. Each n-type semiconductor has a high temperature portion, which functions as a positive pole, and a low temperature portion, which functions as a negative pole. To generate a large amount of electric power, the n-type and p-type semiconductors are alternately connected in series to form an electrode module.
Japanese Laid-Open Patent Publication No. 2000-297632 describes an example of an application of such a thermoelectric generation element. More specifically, a catalyst device (device including a carrier carrying a catalyst for purging exhaust) is arranged in an exhaust passage for an internal combustion engine. A thermoelectric generator is arranged upstream from the catalyst device to convert the thermal energy of exhaust to electric energy. However, the thermoelectric generator absorbs heat from the exhaust. This hinders with the heating of the catalyst device and prolongs the inactive period of the catalyst. To prevent such a problem, the thermoelectric generator functions as a heater that heats the exhaust with electric power when the catalyst is inactive in Japanese Laid-Open Patent Publication No. 2000-297632.
However, when the thermoelectric generation functions as a heater, the thermal energy of the exhaust is not converted to electric energy. This reduces the amount of generated power. To cope with this problem, a further thermoelectric generator is arranged downstream from the catalyst device in Japanese Laid-Open Patent Publication No. 2000-297632. The further thermoelectric generator is constantly used to generate power. However, such a structure enlarges the entire exhaust apparatus.